There are several types of large doors currently in frequent use, including: overhead doors, sliding doors, bi-fold doors, and hydraulic mono-fold doors.
Overhead doors (“OHDs”) are formed by 18′-24″ tall by various door width segments that are stacked vertically into a track system that is mounted to the building at the door sides. The track curves into the building above the door opening. Typically, a minimum of 12″ of headroom is required above the door opening; very large OHDs require as much as 36″ of headroom. OHDs frequently include a torsion spring to counter balance door weight. The spring stores energy as the door is closed and releases it as the door opens, thus minimizing the effort required to open the door and reducing closing force. OHDs are often combined with an electric motor and controls that allow the door to be opened remotely. The horizontal seams inherent in OHD panels and the sliding that occurs at door sides often result in significant air infiltration and significant energy losses. OHDs are very competitive when the doors are less than 16′ wide; they become relatively expensive when they are wider than 24′ and widths greater than 30′ are possible but the cost increases rapidly.
Sliding doors are nearly always the lowest cost door option, are notoriously difficult to insulate and weather-strip, require no or very minimal headroom, require substantial side room making them impractical when continuous openings are required, and can be accessorized in a manner similar to the walls which they resemble. Double sliding doors up to 40′ wide×20′ tall are common. Walk doors, windows and a variety of finish materials can be incorporated into a sliding door. Sliding doors that include cross bucks and windows are often used to improve aesthetics of the building.
Sliding doors are available in a number of styles, the most common include single and double sliders. A third style of sliding door that is not as common is referred to as a “quad door.” The sliding door is formed by building a light frame and covering that frame with corrugated steel sheathing. The assembly is very similar to the building wall; the wall segments or “door leaves” are then suspended from rollers running in a horizontal track located above the door. Sliders can occur on the inside or outside of the building wall.
Bi-Fold Doors consist of two full width door segments. In one embodiment, welded tube steel frames sheathed with the same material as the building wall are typically used to form door panel segments. The upper segment is hinged to the building at the top and the lower segment at the bottom. The lower segment is hinged to the upper segment at the top. Rollers located at and typically extending laterally from the bottom corners of the bottom segment engage vertical tracks mounted to the building at the sides of the door opening. Cables or straps are attached to the bottom and top of the door at intervals across the doors width. A winding mechanism shortens the cables or straps' causing the bottom to be lifted toward the top of the door, while the center of the door pushes out as the door is opened.
In the door open position, the bottom bi-fold panel typically hangs 24″-30″ below the hinges mounted at the top of the bottom panel, limiting the available doorway height. Bi-fold doors can be insulated like the building's walls but weather stripping is somewhat difficult because of the lift/sliding motion of the door relative to the door jamb, and the steel frame creates thermal shorts that can significantly impact thermal performance.
Hydraulic Mono-Fold doors use a pair of hydraulic cylinders to open a single monolithic door slab hinged at the top of the slab to a door frame or header. The cylinders are located so that the door is forced to swing away from the building as the cylinders are extended. Only the perimeter of Mono-Fold doors needs to be weather stripped. The door moves directly away from the door jamb which allows effective weather stripping.
The door can be insulated and accessories such as electricity and light can be added to the door much like a stationary wall.
The hydraulic system used to power mono-fold doors is noisy, messy, expensive, and unreliable, cold weather negatively impacts door speed, thermal lock can prevent the doors from opening or closing and it is difficult to force the doors to open level relative to the height of the door.
Storage and manufacturing buildings often require large doors to allow efficient movement of materials and equipment into and out of the structure. The ideal door would provide all of the following features: No head room requirement, minimal side room requirements, the doors should be able to open and close effectively, quickly and safely, low cost, easy incorporation of accessories, including, but not limited to windows and walk doors and it would be easy to insulate and effectively weather-strip.